1. Field of Invention
The present invention relates to a sensor device which measures surrounding conditions, a retrieval device which searches sensor devices via a network, and a relay device which relays between the sensor devices and the retrieval device.
2. Description of the Related Art
Conventionally, there has been provided a sensor network which is a network system for use in observing natural phenomena such as climate and temperature, surveying the conditions in the event of a natural disaster, and managing stocks. In the sensor network, an Internet Protocol (IP) network, for example, is used as a backbone for connecting each of the components such as a sensor and a database, in order to realize a wide range of services.
For connecting a sensor to the network, a sensor node, which is a sensor device incorporating one or more sensors and a network communication function as one, is used.
In order to make use of the sensor network, it is necessary to communicate with sensor nodes which are capable of obtaining information required for an application program or a service, and to collect the derived data at the side of the application program or a service providing apparatus by operating the sensors on the sensor nodes. Moreover, it is also necessary to provide the user with the collected data or the calculation results obtained based on the data, or to control an actuator based on the calculation results.
In this case, the sensors to be actually used for measurement have to be selected and specified from among many sensors. Therefore, a search function for searching on sensor nodes is required.
Static property search and dynamic property search are provided for the search on sensor nodes. For example, a sensor network equipped with sensor nodes each having a temperature/humidity sensor and being fixedly set in plural locations can be taken as an example here.
In this case, pre-set location, temperature, humidity and the like are conceivable as the properties of the sensor nodes. Among them, the “location” property is a static property owing to the fact that the sensor node is fixedly set, whereas “temperature” and “humidity” properties are dynamic properties which change depending on the time of measurement.
In the case of searching the sensors that are set within a certain region by use of this sensor network, a retrieval node which searches the sensor nodes and transmits inquiry data requesting positional information to all the sensor nodes, and causes the sensor nodes located within the target region to return response data. Based on this, a conceivable method is one in which the retrieval node side lists up the respective sensor node addresses indicated in the response data. However, in a sensor network in which many sensor nodes are set, because the area in which broadcasting is performed is spread out, the communication bands are overloaded and wasteful expenses arise, and thus the abovementioned method is not realistic in terms of scalability.
This is why a method using database, as shown in FIG. 1, is conventionally used.
FIG. 1 is a diagram showing an outline of the conventional sensor network utilizing database for the search of sensor nodes.
In the sensor network 205 shown in FIG. 1, a database 204 manages a correspondence table which associates the positional information of sensor nodes 202 and 203 with the addresses thereof. A retrieval node 201 performs database retrieval, setting positional information as a search condition. The retrieval node can thus list up the addresses of the sensor nodes which fall within the search condition, without making an inquiry to the sensor nodes 202 and 203.
Such a technique in which a sensor network utilizes a database to conduct a search on sensor nodes has been disclosed (e.g. Patent Reference 1).
A sensor network that searches the sensor nodes utilizing a multi-cast communication is provided as a sensor network that searches sensor nodes without making an inquiry to each sensor node.
In such a sensor network, each sensor node is equipped in each automatic dispenser. A sensor in each of the sensor nodes aims to count the remaining quantity for each type of juice placed in an automatic dispenser, and each type of juice is associated, on a one-to-one basis, with a channel address in the multi-cast communication. Also, the information indicating this association is also placed on a server on the network together with the positional information of each automatic dispenser.
The retrieval node receives the type of juice as a search condition, and obtains, from the server, the channel address associated with the search condition. The retrieval node also transmits a reply request to the obtained channel address. The reply request transmitted to the channel address ensures that only the sensor nodes which participate in the channel corresponding to that channel address are targeted for processing, e.g., response.
The retrieval node can identify the automatic dispensers to be searched for, based on the responses received from the respective automatic dispensers.
Thus, in the case of using the multi-cast communication, there is no need for the retrieval node to transmit a reply request to each sensor node. The sensor nodes which do not participate in the channel to be used for the transmission of the reply request do not need to perform processing, e.g., analysis on the reply request. In the case where a sensor node is placed on the network under a router, a reply request goes through the filtering performed by the router so that the reply request of the channel in which the sensor node under the router is presently participating can pass the router. Therefore, the reply request which is unnecessary for the network under that router shall not pass through.
Such a technique regarding the sensor network utilizing multi-cast communication has also been disclosed (e.g. Patent Reference 2).    Patent Reference 1: Japanese Laid-Open Patent Application No. 2004-173108    Patent Reference 2: Japanese Laid-Open Patent Application No. 2004-200821